The 5th match will not solve the problem as long as an even number of games is played in each match.

A few new ideas:

a) One extra game in one of the matches in case of 2-2 (or 2,5-2,5 in case we accept 5 players matches). This game is played at the end of the match just in case the clash ends in a tie.
a,1) The tie-break match is one random match of the clash
a.2) The tie-break match is the "first board" match. This will help let the better players play against each other.

b) In case of 2-2 (or 2,5-2,5) the first board match is worth 4 points, second board match 3 points, etc...This is quite common in chess team championships, and will ad some strategy in the line up

All this said, my opinion (and that doesn't mean CAT opinion) is:
For the final - CL tie break pointed by dea
For the rest: b) first and after a.2)